Significant advances toward the cure of human cancer have been achieved in rapidly growing cancers such as childhoold tumors and Hodgkin's disease. The relatively slow growing solid tumors (e.g. lung, colon and breast carcinomas) have responded poorly to existing chemotherapeutic agents. By understanding the biological responses of the subpopulations of solid tumors to chemotherapy, effective treatment regiments may be designed to attack each population. One important biological subpopulation of neoplastic cells present in solid tumors is the hypoxic tumor cell. Data from our laboratroy indicate that neoplastic cells in hypoxic tumor cell. Data from our laboratory indicate that neoplastic cells in hypoxic environments cannot maintain the integrity of their own DNA, have difficulty in repairing at least two kinds of DNA damage, have lower levels of glutathione, and may be more sensitive to the mutagenic effects of some chemicals when these hypoxic cells are compared with normally aerated cells. The overall goal of this research is to understand the biological responses of neoplastic cells to conditions of low oxygen and to understand the biochemical and pharmacological parameters which influence the responses of these hypoxic tumor cells to cytotoxic drug therapy. To accomplish this goal, we intend to determine the ability of hypoxic cells to accumulate and repair DNA damage during severe and moderate hypoxia; to determine the ability of hypoxic tumor cells to repair mitomycin C induced DNA damage under continued hypoxic exposure or under reoxygenated conditions and to correlate the repair of damage with altered cell survival; to determine the ability of hypoxic tumor cells to restore glutathione levels after depletion by hypoxia, diethylmaleate or by buthionine-S, R-sulfoximine; to assess the ability of hypoxic cells to maintain adequate levels of ATP; and to determine the susceptibility of hypoxic cells to mutation as a measure of their potential to become resistant to chemotherapeutic agents. Colony formation assays, alkaline elution techniques, high performance liquid chromatography, and mutation assays wil be used to assess cell survival, DNA damage, adenine nucleotide levels, and mutation.